1. Field of the Invention
The invention relates to couplings for rigidly connecting two substantially coaxial machine elements, such as two shafts, for example, and which coupling is particularly suitable for transmitting torque. The coupling comprises two coupling members whose adjacent faces are clamped against each other.
2. Description of the Prior Art
Flange couplings are examples of known couplings of this kind. In these, the coupling members are formed as flanges with flat faces that are arranged normal to the axis of rotation and that press against each other. The coupling members are clamped together by bolts or similar connecting devices. The transmission of torque is effected purely by friction-locking, produced by tensile loading of the bolts. The torque which can be transmitted by these couplings is restricted when, due to lack of space, the flanges cannot be constructed as large as necessary.
It is known, e.g. from German Patent No. 1,066,818, to use tapered bores for attaching wheels, discs and the like to a shaft. Friction-locking couplings with complementary cone shaped friction surfaces are also known. It is known that is this type of coupling, where the coupling members press against each other via cone shaped faces instead of via flat faces, there is an increase in the clamping force exerted, so that greater torque can be transmitted. However, cone shaped clamping surfaces have the disadvantage that they may require a great deal of space in the axial direction. In addition, cone shaped complementary surface are expensive to produce as they have to be machined very accurately.
For these reasons, many other types of couplings are known in which other means are used to increase the torque which can be transmitted. For example, fitted bolts may be used and they may be inserted between the faces of the coupling members (see the journal "Konstruktion 1977", page 427, left-hand column), radial serrations may be formed (see German Patent No. 440,816), or tapered pins may be arranged to point in the radial direction between the coupling members (see German Patent No. 1,450,160). By any of these means, the friction-locking connection is supplemented or replaced by a form-locking connection. Couplings of this type are similarly expensive to produce. Some of these known couplings are also sensitive to impact or fluctuating torque, especially the coupling with a key. A coupling with radial serrations has the disadvantage that it produces a high axial thrust when transmitting torque.
In another known type of form-locking coupling (see German Patent No. 635,207), spiral ribs and grooves which engage in each other are machined in the faces of the flanges.
Moreover, other proposals have recently been made for form-locking couplings, especially for linking a universal jointed shaft with the shafts adjoining it. According to German Laid-Open Specification No. 25 54 574, the flanges of a flanged coupling have several groups of parallel teeth which mutually engage in each other. According to German Utility Model No. 77 05 744, the contact surfaces of the two flanges of a coupling lie in a plane which is determined by the axis of rotation. These proposals also have the disadvantage of high production costs.
In addition, it is common to all types of form-locking couplings that the coupling members cannot be assembled in any random position. They must first be brought into the correct relationship by rotating one member relative to the other.